1. Field of the Invention
The present invention relates to a liquid supply device and an image forming apparatus, and more particularly to a structure of a sub tank used in a liquid supply device installed in an inkjet recording device.
2. Description of the Related Art
Conventionally, there is an inkjet recording device among image forming apparatuses such as a printer, a fax machine, a copier, and a plotter. In the inkjet recording device, a low-volume sub tank (liquid container) for supplying ink (liquid) to an inkjet head (liquid jet head) is provided on a carriage, and a high-volume ink cartridge (main tank/liquid storing tank) is provided in the main body of the inkjet recording device. Accordingly, the sub tank is replenished with ink supplied from the main body.
In the above configuration using a sub tank, there is no need to install a large ink tank on the carriage, and therefore when the carriage is moved, the kinetic load for driving the carriage can be reduced and the carriage can be prevented from oscillating.
The ink (liquid) in the main tank is supplied to the sub tank with the use of predetermined pressure. The inside of the sub tank has a negative pressure tendency so that ink is prevented from needlessly flowing to the nozzles. Accordingly, the ink is prevented from needlessly flowing to the head, so that liquid is prevented from dropping out.
FIGS. 10A and 10B illustrate a mechanism for supplying ink to a sub tank having a negative pressure tendency, which is disclosed in patent document 1.
As shown in FIGS. 10A and 10B, the negative pressure in a negative pressure chamber 101 in a sub tank 100 is generated as a flexible member such as a film 102 is expanded outward by a spring 103. Specifically, the spring 103 does not directly push the film 102, but rather, the spring 103 pushes a disk-type sheet 104 that is welded to the film 102 for the purpose of reinforcing the film 102.
At a position facing the disk-type sheet 104 across the film 102, a force is generated at a point of effort 108A of a lever member 108. A valve member 105 is provided at a point of load 108B. The valve member 105 is operated via a fulcrum 108C to open an ink injection part 100A. Accordingly, the ink in a supply path connected to the main tank is supplied to the negative pressure chamber 101. The valve opening pressure of the valve member 105 is set to a static pressure by a spring 107.
The above configuration uses the function of a lever, and therefore it is possible to generate a force that is greater than or equal to the pressure-receiving area of the film 102.
There is proposed a mechanism for preventing the oscillation of a film in a structure using the film. Specifically, flexible films and resin plates that are integrally combined with the flexible films are used as walls of the sub tank. Accordingly, the oscillation of the flexible film can be mitigated by the resin plates (see, for example, patent document 2).
In a configuration in which the sub tank and the ink tank are placed at different positions, and the sub tank and the ink tank are connected by a tube, the following problem may arise. That is, as the main scanning width increases, the length of the tube needs to be increased. Accordingly, inertia occurs when the speed of the carriage is increased or decreased. Due to this inertia, the ink moves, and the liquid pressure changes from a predetermined pressure. Changes in the liquid pressure affect the negative pressure tendency in the sub tank. Consequently, the liquid ink may needlessly drop out from the head.
Patent Document 1: Japanese Laid-Open Patent Application No. 2005-096404
Patent Document 2: Japanese Laid-Open Patent Application No. 2008-143027